Process of purifying sugar juices



April 10, 1934. J. P. FOSTER 1,954,565

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# za, Mmc/ Patented Apr. `10, 1934 VUNITED STATES l Laatstey V--PMEN'P OFFICE This invention relates to processes of purifying sugar juices and it comprises a process wherein raw sugar juice, such as that from beet or cane sources, is first treated with lime to render the l juice highly alkaline and thereafter the limed juice without the application of heat thereto, is subjected to centrifugal separation by means of which insoluble constituents are separated; it further comprises a process wherein the muds coming from the centrifugal are'diluted, partially neutralized, filtered, the clear filtrate united with partially neutralized clear liquid from the `centrifugal and the whole filtered and further treated to render it suitable for concentration and crystallization of the sugar therein; and it further comprises processes wherein the highly alkaline limed juice is centrifuged, the muds therefrom diluted, partially neutralized and ltered, the filtrate united with the clear juice flowing from.

the centrifugal, and the resulting mixture of juice carbonated to approximate neutrality and further treated to flt it for concentration vand crystallization.

Raw sugar juices contain, in addition to the sugar dissolved therein, impurities collectively referred to as non-sugars. These non-sugars are largely colloidal in character. Some of them are complex iron compounds, others are of an albuminous nature. If left in the juice, they inhibit crystallization of the sugar and they must therefore be removed prior to concentration. Many processes have'been proposed to this end, but it is invariably the practice to add relatively large quantities of lime, quantities far in excess of that necessary to neutralize the natural acidity of the juice, and then, by carbonation with carbon dioxide, remove the excess lime together with nonsugars in the form of insoluble lime compounds.

Merely adding lime does not suffice to remove 40' non-sugars. Although insoluble lime compounds are formed, they are not readily iiltered even when a lter aid such as kieselguhr is added. Heating the limed juices vto flocculatethe insoluble non-sugars tends to destroy the sugar in the juice. Carbonation is customarily resorted to to yield a iilterable precipitate as Well as remove excess lime. However, lime also forms insoluble compounds with the sugar itself and these compounds are converted into calcium-sugar-carbonates on carbonation of the highly alkaline juices.

Carbonation also tends to dissociate the calciumnon-sugar compounds and return the latter to the solution although under carefully controlled conditions, the carbonation may be so regulated that the calcium-sugar compounds only are dis-- enough. Accordingly, the art has been obliged to content itself with liming and carbonation, accepting loss of available sugar, excessive foaming, loss of time in processing and other inherent disadvantages as something which must be endured.

It is an object of this vinvention to provide a process wherein cold defecation can be realized. I have now found that the insolubles in cold limed juice can be separated in a centrifugal type of separator. While centrifugal machines have been used in processes of purifying sugar juice, to my knowledge, no one has previously appreciated that the cold limed juice without heatingcould be separated from the insolubles therein by means of a centrifugal type of separator. As stated, the universal practice has been to lime the juices and then heat or carbonate the limed juice to coagulate non-sugars prior to attempting any separation of any kind. The use of a centrifugal separator to separate the insoluble nonsugars in the cold limed juice has enabled me to remove the non-'sugar compounds without resort to heat` and to recover all of the sugar in the calcium sugar compounds formed during the liming operation. Since no heat is employed, these insoluble sugar compounds can b separated from the limedjuice without losses due to decomposition and thereafter the sucrose easily' recovered as will be more fully hereinafter' described. I regard the use of a centrifugal separator 'to separate the insoluble non-sugars from cold limedv juices as one of the fundamental concepts in my invention and it has proven especially Valuable in conjunction with the advantageous series of process steps presently to be described.

While centrifugal separators are commonly used in various unrelated arts to separate insoluble constituents from asuspension thereof in a liquid medium, I iind that the use of such a separator in my process leads to quite new and unexpected results, particularly since prior workers in this art have unanimously considered cold defecation to be. impracticable in practice because the insoluble products of cold defecation could not be separated from the residual sugar juices. Prior to this invention centrifugal'separators have been used in sugar processes only as substitutes for an ordinary filter when separating fiocculated insolubles from heated limed juices.

In my process, I find it advantageous to treat sugar juices in a series of steps wherein the juices are first limed to high alkalinity, then, without heating, centrifuged, and the mud of non-sugars and calcium-sugar compounds worked up to recover sugar therefrom.

On the foregoing single sheet of drawings I have indicated diagrammatically in flow sheetv form two ladvantageous ways of putting my invention into practice. For clearness, reference should be had tothe drawing as the following description proceeds.

Referring more particularly to process A cold cane sugar mill juice at ordinary temperature, not to exceed to 50 C., is first limed with, for example, ten percent of twentyy degree Baume milk of lime. This will give the juice an alkalnity of about pH 14. This limed juice now contains insoluble compounds of lime and non-sugars as well as insoluble calcium compounds of sugar. Because it is coldit cannot be filtered in an ordinary flter press and, as stated, such ju'ces are 'generally heated to coagulate the insolubles or carbonated to form calcium carbonate. In my process, I depart from the teachings of the prior art at'this point and directly pass the cold limed juice to a centrifugal designated at 2. In practice I nd that centrifugal separators of the Kopke j type are advantageously employed. These separators are well known in the sugar industry and are familiar to the sugar mill operator so that furtherl description is unnecessary. Other separators of the centrifugal type can of course be used.

In the centrifugal, insolubles are separated from the juice and the insoluble cold mud is passed by way of line 7 to a tank 8. The 'run-off juices from the centrifugal, now freed of insolubles, flow through line 3 to tank 4. In tank 8, or during the passage from the centrifugal to`tank 8, the cold mud is diluted with cold water. The diluted mud in 8 is then partially neutralized with anacid until the pI-l. value is about 10.5. Sulphur dioxide is advantageously used for this purpose since it does not enter into combination with the calcium-sugar compounds. 'Carbon dioxide can, however, be used.- The sulphur dioxide acts to dissociate the calcium-sugar compounds with the liberation of sugar which returns to the solution. In this way the sugar is recovered without loss. By controlling the extent of acidification so that the hydrogen ion concentration does not fall much below pH 10.5 the insolublev calcium compounds of the non-sugars are not decomposed so that these may subsequently be separated from the sugar solution thus obtained. The diluted mud having a pH value of about 10.5 is then passed by Way of line 9 to a second centrifugal separator 10. An ordinary filter can be used at this point but I find that a centrifugal separator glves abetter and faster, separation. The mud is dis-` charged by way of line 11 from centrifugal 10 and consists of the insoluble non-sugars. The clear solution leaving the centrifugal 10 by way of line 12 contains the sugar originally in the mud ycoming from centrifugal 2.

The clear juicecoming from centrifugal 2 by way of line 3 is passed to a tank 1 wherein it is united with the sugar solution coming from the separator 10, and the mixed juices are carbonated With.carbon dioxide until the pI-I value is about 8.5. It will be remembered that this juice is highly. alkaline and is substantially free of the non-sugars in the original juice. Carbonation in tank 4 is for the purpose of removing a large portion of the excess lime and is continued until the acidity is increased to about pH 8.5. The carbonated juice is then passed through line 5 to filter 6. The mixed juice is then filtered from calcium carbonate. The so-called lime cake formed in the filter 6 is discarded and the clear filtrate lightly limed during its passage through line 13 to carbonation tank 14. Here the limed juice is carbonated to neutrality and thence passed by way of line 15 to lter 16. The clear juice then flows by line 17 to tank 18 where it is decolorized with carbon, passes to filter 20 through line 19 and finally goes to the boiling house where the purified and decolorized juice is concentrated.

In process B as shown on the drawing, I have indicated another advantageous series of process steps wherein the centrifugal separation of cold limed juice is employed.

In this alternative process, cold limed juice is conducted to centrifugal 2 by pipe 1. The mud from the centrifugal is passed by line '7 to tank 8 wherein it is diluted and treated with sulphur dioxide as described in connection with process A. The partially neutralized diluted mud from tank 8 is then conducted by way of line 9 to a lter or second centrifugal 10 wherein the nonsugars are thrown out and discarded and the clear solution of recovered sugar run off. This solution flows through line 12 to a tank 21 wherein it is mixed with the clear* juice coming from centrifugal 2 through line 3. In tank 21 the mixed juices are carbonated with carbon dioxide until substantially neutral and then the cold carbonated juice is passed to lter 23 by way of line 22 wherein the calcium carbonate is separated. The clear juice is then decolorized with carbon in tank 24, ltered in filter 25 and passed to the dering beet juice fllterable or avoiding decom position of cane juice constituents. In my process, the centrifugal separation functions as a sort of primary carbonation thus making process A in eect a triple carbonation and process B a double carbonation without the disadvantages of actually carrying out additional carbonation steps.`

While I have described what I find to be the most advantageous way of carrying out my process, I do not of course wish to be limited thereto other thanas the prior art may dictate. It

is of'course understood that the quantities of lime to be added to the raw juice will vary with the nature of the juice and the hydrogen ion concentration to which the juice is adjusted will also varyin accordance with requirements. It should also be understood that other ways of continuing the purification of the centrifuged cold limed juice can be employed.

In the appended claims, I have dened the iii) juice as "unheated in this way distinguishing from prior processes wherein the juice is heated prior to a separation step. By unheated juice I mean the juice at its ordinary temperature, preferably not exceeding 40 to 50 C.

What is claimed is:

1. In the process of purifyingraw sugar juices,

the steps which comprise liming the juice to high alkalinity such that substantially all of the non-sugars become substantially insoluble and then before reducing the alkalinity subjecting the limed, unheated juice to centrifugal separation to separate insoluble -substances therein from the juice. 2. In the process 'of purifying raw sugar juices the steps which comprise liming the juice to high alkalinity such that-substantially all of the nonsugars become substantially insoluble, subjecting the limed, unheated juice to centrifugal separation before reducing the alkalinity to separate insoluble substances as a` mud and to obtain a clear alkaline juice, diluting and partially neutralizing the mud to dissociate calcium-sugar compounds therein and return sugar to solution Without substantially dissociating the calciumnon-sugar compounds, and then separating the residual insoluble substances from the sugar solution thus obtained.

3. Inthe process of purifying raw sugar juices, the steps which comprise liming the juice to high alkalinity such that substantially all of the nonsugars become substantially insoluble, subjecting the limed, unheated juice `to centrifugal separation before reducing the alkalinity to separate insoluble substances therein as a mud and to obtain a clear alkaline juice, carbonating the clear juice with carbon dioxide, diluting the mud, partially neutralizingthe mud to dissociate calcium-sugar compounds and return sugar to solution without Vsubstantially dissociating the calcium-non-sugar compounds, separating residual insoluble substances from the thus formed sugar solution and uniting and ltering the latter with the aforementioned carbonated juice.

4. In the process of purifying raw sugar juices, the steps which comprise liming the juice to high .alkalinity such that substantially all of the nonsugars become substantially insoluble, subjecting the limed, unheated juice to centrifugal separation before reducing the alkalinity to separate insoluble substances as a mud and to obtain a clear alkaline ltrate, diluting and partially neutralizing the mud to recovered combined sugar therein as a solution Without substantially dissociating the calcium-non-sugar compounds, separating residual insoluble substances from the solution, uniting the clear sugar solution thus obtained with the aforementioned alkaline juice, and carbonating the united liquids.

, 5. In the process of purifying raw sugar juices, the steps which comprise liming the juice to high alkalinity such that substantially all of the nonsugars become substantially insoluble, subjecting the limed, unheated juice to centrifugal separation before reducing the alkalinity andcarbonating the clear alkaline juice thus obtained.

6. In the process of purifying raw sugar juices, the steps which comprise liming the juice to high alkalinity such that substantially all of the nonsugars become substantially insoluble, subjecting the limed, unheated juiceI to centrifugal separation before reducing the alkalinity to separate insolublesubstances therein as a mud and to obtain a clear alkaline ltrate, carbonating the filthe limed, unheated juice to centrifugal sep'aration before reducing the alkalinity to separate insoluble substances therein as a mud, diluting the mud, treating the diluted mud with sulphur dioxide until the pH value is about 10.5 but greater than that at which calcium-non-sugar compounds are dissociated, and then separating the insoluble calcium-non-sugar compounds from the sugar solution thus obtained.

8. In the process of purifying raw sugar juices,

the steps which comprise liming the juice to high Yalkalinity such that substantially all of the nonsugars become substantially insoluble, subjecting` .the limed, unheated juice to centrifugal separation before reducing the alkalinity to separate insoluble substances therein as a mud, diluting the mud, treating the diluted mud with sulphur dioxide until the pH value is about 10.5 but greater than that at which calcium-'non-sugar compounds are dissociated, separating the insoluble calcium-non-sugar compounds from the sugar solution thus obtained, uniting the sugar solution with the clear alkaline juice resulting from the aforementioned centrifugal separation, and carbonating the united solution and juice to approx- -imate neutrality.

. JOHN P. FOS'IYER.` 

